Permanent and Switched Virtual Circuits

The end-to-end (DTE to DTE) connection provided by the X.25 Recommendations is called a virtual circuit. This is not a physical connection between the DTEs; it is a logical communication path. Public networks offer two types of virtual circuit--permanent and switched. Typically a subscription consists of a mixture of the two.

A permanent virtual circuit (PVC) is a permanent association between two DTEs that is established when a user subscribes to a public network. Many providers charge a flat rate per month for a PVC in addition to the charge per unit of data.

A switched virtual circuit (SVC) is a temporary association between two DTEs that exists only for the duration of a call. Most providers charge per minute for an SVC in addition to a charge per unit of data.

In general, SVCs are less expensive than PVCs unless two end-points need to be in constant communication, but this varies between providers depending on their tariff structure.

SVCs and PVCs can both be used across both dial-up and leased lines. However, using a PVC with a dial-up line is unlikely to be useful.